1. Field of the Invention
The present invention relates to an actuator for adjusting the pitch angle of a rotor blade of a wind turbine, which is rotatably mounted on a rotor hub, comprising a first drive element connectable with the rotor blade, a second drive element in meshing engagement with said first drive element, as well as a lubricating device for lubricating the two drive elements. The invention furthermore relates to a rotor with a rotor hub, on which at least one rotor blade is rotatably mounted, whose pitch angle can be adjusted by an actuator as mentioned above. Finally, the invention relates to a wind turbine comprising such rotor and such actuator.
2. Description of the Prior Art
Wind turbines regularly employ rotors whose rotor blades are rotatably mounted on the rotor hub, so that the pitch angle of the rotor blades can be adjusted. By means of large roller bearings, the rotor blades can be mounted at the rotor hub so as to be rotatable about their longitudinal axis, so that an actuator accommodated inside the rotor hub can change the pitch angle of the rotor blades. For this purpose, so-called pitch drives are used, as they are disclosed for instance in DE 200 17 994 U1. Preferably, the drive movement of an actuator motor is transmitted to the rotor blade via a gear stage. Advantageously, the rotor blade can be flanged directly onto the inner ring of the large roller bearing, which constitutes a stewing ring and has an internal toothing with which a drive pinion is meshing, which is arranged inside the slewing ring and is seated on a drive shaft.
Of course, the actuators in such rotors of wind turbines must be lubricated. An example for a lubricating device in the rotor of a wind turbine is shown for instance in DE 200 21 026 U1. A lubrication problem arises for instance in that the pitch angle of the rotor blades is not frequently changed, as there is an optimum pitch angle for the rotor blades over a wide wind range, so that the rotor blades actually are only twisted when the wind is too strong or the turbine must be stopped for maintenance purposes. This leads to the fact that the actuators remain in the same position for most of the operating time, and in the gear stage of the actuator always the same pair of teeth of the meshing drive elements is in engagement with each other. The lubricant thereby can be displaced, so that an increased wear occurs at this pair of teeth. The pair of teeth of the stewing ring and of the drive pinion, which is in engagement with each other in the optimum pitch angle position of the rotor blades, often is also referred to as pair of zero teeth or as zero tooth. These zero teeth of the drive elements in the wind turbine rotors gradually suffer from chipping at their tooth flanks and exhibit strong wear after some time. The torques resulting from the attack of wind must always be tolerated at the same point of attack, which is even aggravated by vibrations and oscillations likewise suffered by the tooth engagement.
To avoid these problems it has already been proposed to offset the meshing drive elements with respect to each other after some time, so that in the working position of the rotor blade they are meshing with other teeth. In the case of wind turbines, however, this is not easily possible merely because of the enormous dimensions of the turbine. A disassembly of the rotor blade is extremely time-consuming. Even inside the rotor hub, the actuator cannot easily be repositioned. Therefore, it has already been considered to provide the meshing drive elements with an associated lubricating wheel which meshes with one of the drive elements and transfers lubricant onto the same. From time to time, the actuator is operated, in order to thereby ensure lubrication. However, such design of the lubricating device is very costly. In addition, the pitch angle of the rotor blades must be changed at undesired times.